For those who don’t know, SHSH Blob is a signature verification file against Apple Server. It verifies that the iDevice is running the latest version of iOS. Saving SHSH blobs will allow you to restore to previous version. While doing so Apple will stop you doing the restore process. To make this happen you have send a request to different servers which forwards SHSH blobs to iTunes by just showing it that its a new version of iOS. This is how TinyUmbrella or iSHSHIT works to help you save SHSH blobs.